Semiconductor device having a gate that is buried in an active region and a device isolation film

ABSTRACT

A semiconductor device includes an active region with a first gate trench formed when a gate region is etched to a first depth, a device isolation film defining the active region and including a second gate-trench formed when a gate region is etched to a second depth, a gate buried below the first gate trench and the second gate trench, and a source plug and a drain plug formed when a conductive material is deposited in a source region and a drain region of the active region.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 14/340,489 filed on Jul. 24, 2014 and now issued as U.S. Pat. No.9,401,301, which claims the priority of Korean patent application No.10-2014-0036798 filed on 28 Mar. 2014, the disclosures of which arehereby incorporated in their entireties by reference.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to a semiconductor devicehaving a fin channel.

As the integration degree of semiconductor devices increases, a designrule is reduced, such that the semiconductor device has difficultymaintaining a stable operation of transistors.

Specifically, as the size of an active region is reduced in a widthdirection, drive current characteristics are deteriorated, resulting inthe occurrence of Write-Recovery Time (tWR) deterioration.

A more extended current path improves a drive current of the cell. A finField Effect Transistor (FinFET) has been used to secure a presentcurrent path.

However, there are limits to the amount that a conventional fintransistor can improve drive current and channel resistance by simplyincreasing fin increases in height. In addition, it is difficult toincrease a drive current simultaneously while maintaining the ratio ofwidth to length of a channel in a conventional fin transistor.Furthermore, it is difficult to construct a junctionless transistorusing conventional technologies.

BRIEF SUMMARY OF THE INVENTION

Various embodiments of the present invention are directed to providing asemiconductor device having a fin-type channel (fin channel) and amethod for forming the same that substantially obviate one or moreproblems due to limitations and disadvantages of the related art.

An embodiment of the present invention relates to a technology forextending a path of a drive current by improving a structure of asemiconductor device having a fin channel, resulting in improvement ofthe drive current of the semiconductor device.

In accordance with an aspect of the present invention, a semiconductordevice includes: an active region including a first gate trench having afirst depth; a first device isolation film defining the active region,and including a second gate trench having a second depth; a gatedisposed in the first gate trench and the second gate trench; a sourceplug buried in a source region of the active region, the source plugincluding a conductive material; and a drain plug buried in a drainregion of the active region, the drain plug including the conductivematerial.

In accordance with another aspect of the present invention, a method forforming a semiconductor device includes: forming a device isolation filmdefining an active region; forming a gate trench by etching the activeregion and the device isolation film; forming a buried gate in a lowerportion of the gate trench; forming a source recess and a drain recessby etching a source region and a drain region of the active region; andforming a source plug and a drain plug by depositing a conductivematerial into the source recess and the drain recess.

It is to be understood that both the foregoing general description andthe following detailed description of embodiments are exemplary andexplanatory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a semiconductor device according toan embodiment.

FIG. 2 illustrates two cross-sectional views taken along lines A-A′ andB-B′ of FIG. 1

FIGS. 3 to 10 are cross-sectional views illustrating a method forforming the embodiment of FIGS. 1 and 2. Each of FIGS. 3 to 10 show twocross sectional views which correspond to the lines A-A′ and B-B′ ofFIG. 1.

FIG. 11 illustrates cross sectional views of a semiconductor deviceaccording to another embodiment corresponding to lines A-A′ and

B-B′ of FIG. 1.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to certain embodiments, exampleswhich are illustrated in the accompanying drawings. The same referencenumbers refer to the same or like parts. In the following description, adetailed description of well-known configurations or functions may beomitted. Embodiments described in the specification and shown in thedrawings are purely illustrative and are not intended to represent allaspects of the invention.

FIG. 1 is a plan view illustrating a semiconductor device according toan embodiment. FIG. 2 shows two cross-sectional views taken along linesA-A′ and B-B′ of FIG. 1.

Referring to FIGS. 1 and 2, an active region 102 formed by etching asemiconductor substrate 100 is defined by a first device isolation film104 a and a second device isolation film 104 b. The first deviceisolation film 104 a is arranged parallel to a long-axis direction ofthe active region 102 and a line shaped second device isolation film 104b is arranged parallel to a buried gate 106, thereby isolating adjacentactive regions 102 from each other. Several active regions 102 arrangedadjacent to each other and spaced apart along a long axis of the buriedgate 106. Each active region 102 may be coupled to two buried gates 106.A plurality of parallel and adjacent active regions 102 may be coupledto the same two buried gates 106, while a neighboring set of paralleladjacent active regions 102 are coupled to a next two buried gates 106.

Each active region 102 crosses two buried gates 106 and one bit line108. In an embodiment, the active region 102 crosses the buried gates106 and the bit line 108 at oblique angles, and the buried gates 106cross the bit line 108. The buried gates 106 are buried in a linear gatetrench etched in gate regions of the active region 102 and the firstdevice isolation film 104 a. In an embodiment, the gate trench in whicheach buried gate 106 is disposed has a fin structure in which the activeregion 102 protrudes further from the substrate 100 than the firstdevice isolation film 104 a because the first device isolation film 104a is more deeply etched than the active region 102. Therefore, theburied gate 106 is disposed over three sides of the active region 102.In an embodiment, a height of a fin structure is greater than a heightof the gate 106 formed over the protruded active region (fin) 102.

The embodiment shown in FIG. 2 includes a plurality of source and drainplugs 110. The source and drain plugs 110 may be formed by depositing aconductive material in source and drain regions of a transistor. Bottomsurfaces of the source and drain plugs 110 may define upper shoulders offin-shaped active regions 102, and the shoulder height may besubstantially level with a bottom surface of the gate 106 buried in thedevice isolation film 104 a.

In other words, in an embodiment, source and drain regions are notformed by a conventional process of simply depositing different types ofimpurities into source and drain regions. Instead, recesses are beformed by etching source and drain regions to a fin depth and depositingconductive materials in the source and drain regions to form source anddrain plugs 110. The conductive material may be a doped polysilicon ormetal. Here, the fin depth is the height above which the active region(fin) protrudes above the first isolation film 104 a.

A channel region 112 is disposed below the buried gate 106 in a portionof the active region 102 interposed between the source and drain plugs110. As seen in FIG. 2, the source and drain plugs 110 are disposed atthe same depth as a shoulder between adjacent fins such that a drivecurrent may flow across an entire fin height as indicated by thehorizontal arrows.

In other words, channel regions 112 surrounded by the buried gates 106extend for the entire height of fins protruding from the deviceisolation film 104 a. Accordingly, the amount of a drive current flowingin the channel region 112 for use in a semiconductor device according toan embodiment increases in proportion to the height of fin.

In an embodiment, the channel region 112 includes the same kind ofimpurity as the source and drain plugs 110. In such an embodiment, thesource and drain region 110 and the channel region 112 may include thesame kind of impurity, such that a transistor can be driven as ajunctionless transistor. In this embodiment, the entire channel region112 can be fully depleted by a gate voltage(negative voltage).

FIGS. 3 to 10 show cross-sectional views corresponding to lines A-A′ andB-B′ of FIG. 1 illustrating a method for forming a semiconductor devicesaccording to an embodiment.

Referring to FIG. 3, a hard mask layer (not shown) is formed over asemiconductor substrate 200. The hard mask layer may include an oxidefilm.

Subsequently, after an ISO mask pattern (not shown) defining line-typeactive regions is formed over the hard mask layer, the hard mask layeris etched using the ISO mask pattern as an etch mask, such that a hardmask pattern (not shown) is formed. The ISO mask pattern may include aphotoresist pattern, and may be formed by a Spacer Pattern Technology(SPT) process.

The semiconductor substrate 200 is etched using the hard mask pattern(not shown) as an etch mask, thereby forming a first device-isolationtrench (not shown) defining a plurality of active regions 202 arrangedin parallel lines. The active regions 202 may be arranged in lines thatobliquely cross with a bit line and gate (word line) formed insubsequent processes.

Subsequently, an insulation film for device isolation is deposited tofill the first device-isolation trench, thereby forming a first deviceisolation film 204 defining line-type active region 202. The firstdevice isolation film 204 may include a Spin On Dielectric (SOD)material having superior gapfill characteristics or a High DensityPlasma (HDP) oxide film. In other embodiments, the device isolation film204 may be formed of a nitride film, or may be formed of a stackedstructure of an oxide film and a nitride film. Before forming the firstdevice isolation film 204, a sidewall oxide film may be formed over asidewall of the first device-isolation trench.

Referring to FIG. 4, an ISO cut-mask pattern (not shown) for cutting (orisolating) the line-type active region 202 in units of a predeterminedlength is formed over the active region 202 and the first deviceisolation film 204. Subsequently, the active region 202 and the firstdevice isolation film 204 are etched in a line shape using the ISOcut-mask pattern as an etch mask, such that a second device-isolationtrench 208 is formed to define an island-type active region 206. In anembodiment, the second device-isolation trench is formed in a line shapethat extends parallel to a buried gate that is formed in a subsequentprocess.

Referring to FIG. 5, a device-isolation insulation film is deposited tofill the second device-isolation trench 208 and then planarized, therebyforming a second device isolation film 210 that defines the island-typeactive region 206. In other words, the first and second device isolationfilm 204 and 210 are formed so that a plurality of island-type activeregions 206 are arranged parallel in a line. In an embodiment, thesecond device isolation film 210 includes a nitride film, and a sidewalloxide film (e.g., a wall oxide film) may be formed over a sidewall ofthe second device-isolation trench 208 before formation of the seconddevice isolation film 210.

A buried gate (BG) mask pattern (not shown) defining a gate region isformed over the active region 206 and the device isolation films (204,210). This BG mask pattern may include a hard mask pattern.

Subsequently, the active region 206 and the first device isolation film204 are etched using the BG mask pattern as an etch mask, therebyforming a gate trench 212. In an embodiment, the first device isolationfilm 204 is more deeply etched than the active region 206 so that thegate trench 212 has a fin structure in which the active region 206protrudes further from the substrate 200 than the first device isolationfilm 204, and the height (H) of the fin structure is greater than thatof a conventional fin structure.

In more detail, although a fin structure of the conventional art isformed to have a relatively large height, the size of a part in which anactual drive current flows is limited. More specifically, the extent ofthe field effect is relatively limited, so a channel region in aconventional field effect of a transistor has a limited size regardlessof the depth of a fin which carries the channel current. In contrast, asemiconductor device according to an embodiment of the present inventionmay increase the drive current in proportion to the height of fin. Thus,the fin structure of an embodiment includes a fin that is taller than aconventional fin, and the drive current increases in proportion to theheight of fin.

Referring to FIG. 6, a gate insulation film 214 is formed over a portionof the active region 206 exposed by the gate trench 212. The gateinsulation film 214 may include an oxide film. The oxide film may beformed of a high-K material, for example, silicon oxide (SiO₂), siliconoxynitride (SiON), hafnium oxide (HfO₂), tantalum oxide (Ta₂O₅), etc.The gate insulation film 214 may be formed by depositing an oxidematerial over the active region 206, or by oxidizing a surface of theactive region 206 through a dry or wet oxidation process.

Referring to FIG. 7, a gate conductive film is formed over the gateinsulation film 214 to fill the gate trench 212. The gate conductivefilm is then etched back, thereby forming a gate 216 buried in a lowerportion of the gate trench 212. The buried gate 216 may have a fin gatestructure enclosing three sides (a top surface and both sides) of theprotruded active region 206. The gate conductive film may include ametal (e.g., tungsten or titanium) material or a stacked structure of ametal and a barrier metal (e.g., titanium nitride). The portion of theburied gate 216 formed over the active region 206 may have a thicknessof 100 Å or less.

Referring to FIG. 8, a sealing film 218 is formed to fill the gatetrench 212. Here, the sealing film 218 may include a nitride film whichinsulates the buried gate 216.

Subsequently, a source region is etched to form a source recess 220, anda drain region is etched to form a drain recess 222. In an embodiment,the bottom surfaces of the source recess 220 and the drain recess 222may have the substantially same height as a top surface of the firstdevice isolation film 204 etched when forming the gate trench 212. Thatis, the source recess 220 and the drain recess 222 may be formed at adepth corresponding to the depth of a fin.

Referring to FIG. 9, a conductive material is deposited to fill thesource recess 220 and the drain recess 222 and then planarized, therebyforming a source plug 224 in the source region and a drain plug 226 inthe drain region. In other words, according to an embodiment, a sourceregion and the drain are not formed by implanting impurities into theactive region 206. Instead, the source region and the drain are formedby depositing a conductive material in the form of a plug on both sidesof buried gate 216. The source plug 224 and the drain plug 226 mayinclude doped polysilicon or metal. In an embodiment in which a metalmaterial is used as a conductive material for a source and a drain,impurities are implanted in the source recess 220 and the drain recess222 before the conductive material is buried, such that an impuritylayer may be formed in boundary regions between the metal of the sourceplug and drain plug and a channel region of the active region 206.

In an embodiment, a semiconductor device including the source plug 224and the drain plug 226 is annealed, such that the plug material isdiffused into the active region 206.

Referring to FIG. 10, after an interlayer insulation film 228 is formedover the semiconductor device, a bit line contact hole 230 exposing thedrain plug 226 is formed. Subsequently, a conductive material isdeposited in the bit line contact hole 230 to fill the hole and is thenplanarized, resulting in a bit line contact plug 232. The bit linecontact plug 232 may be formed of the same material as the drain plug226. For example, the bit line contact plug 232 may include a dopedpolysilicon material.

Thereafter, a conductive film (not shown) for a bit line and a hard masklayer (not shown) are formed over the bit line contact plug 232. Thebitline conductive film may include a metal (e.g., tungsten or titanium)material or a stacked structure of a metal and a barrier metal (e.g.,titanium nitride).

Subsequently, the hard mask layer and the bit line conductive film areetched using a mask pattern (not shown) defining a bit line region,thereby forming a bit line 234.

In an embodiment in which a polysilicon material is used as a conductivematerial for the source plug 224 and the drain plug 226, the sameimpurities (e.g., N-type impurities) as the source plug 224 and thedrain plug 226 are implanted into an active region (channel region)between the source plug 224 and the drain plug 226, resulting in ajunctionless transistor.

In such an embodiment, the impurity implantation process may include,for example, forming a gate trench 212 as shown in FIG. 5 and implantingimpurities into a lower portion of the gate trench 212.

FIG. 11 is a cross-sectional view illustrating a semiconductor deviceaccording to another embodiment.

Referring to FIG. 11, a bit line 236 is buried in the active region 206and first and second device isolation films 204 and 210 such that thebit line 236 has a buried bit line structure. After a bit line 236 isformed in the active region 206 and the device isolation films, a drainplug 238 is formed to be coupled to the buried bit line 236.

As is apparent from the above description, embodiments of the presentinvention can improve drive current characteristics of the semiconductordevice having a fin channel.

Those skilled in the art will appreciate that embodiments may be carriedout in other ways other than those set forth herein without departingfrom the spirit of this disclosure. The above embodiments are thereforeto be construed in all aspects as illustrative and not restrictive.

The above embodiments are illustrative and not limitative. Variousalternatives and equivalents are possible. The scope of this disclosureis not limited by the type of deposition, etching polishing, andpatterning steps described herein. Furthermore, embodiments are notlimited to any specific type of semiconductor device. For example,embodiments may be implemented in a dynamic random access memory (DRAM)device or nonvolatile memory device. Other additions, subtractions, ormodifications are obvious in view of the present disclosure and areintended to fall within the scope of the appended claims.

What is claimed is:
 1. A method for forming a semiconductor device,comprising: forming a device isolation film defining an active region;forming a gate trench by etching the active region and the deviceisolation film; forming a buried gate in a lower portion of the gatetrench; forming a source recess and a drain recess by etching a sourceregion and a drain region of the active region; and forming a sourceplug and a drain plug by depositing a conductive material into thesource recess and the drain recess.
 2. The method according to claim 1,wherein forming the gate trench includes: etching the device isolationfilm more deeply than the active region so that the active regionprotrudes in a fin structure.
 3. The method according to claim 2,wherein forming the source recess and the drain recess includes: etchingthe source region and the drain region to a depth of the fin structure.4. The method according to claim 2, wherein, in a direction parallel tothe buried gate, the buried gate is over the fin, and a height of aportion of the buried gate over the fin is less than a height of thefin.
 5. The method according to claim 1, further comprising: annealingthe source plug and the drain plug.
 6. The method according to claim 1,wherein forming the source plug and the drain plug includes: depositinga doped polysilicon material or a metal material in the source recessand the drain recess.
 7. The method according to claim 1, whereinforming the source plug and the drain plug includes: implantingimpurities into the source recess and the drain recess; and depositing ametal material in the source recess and the drain recess.
 8. The methodaccording to claim 1, wherein the source plug and the drain plug eachinclude a first type of impurities, the method further comprising:implanting the first type of impurities into a channel region of theactive region disposed between the source plug and the drain plug. 9.The method according to claim 1, wherein forming the device isolationfilm includes: forming first device isolation trenches by etching asemiconductor substrate, the first device isolation trenches defining aplurality of linear first active regions parallel to one another;forming a first device isolation film by depositing a first insulationfilm in the first device isolation trench; forming a second deviceisolation trench defining a plurality of island type second activeregions by etching the first active region and the first deviceisolation film in a direction parallel to the gate; and forming a seconddevice isolation film by depositing a second insulation film in thesecond device isolation trench.